JPH06231771A - Electrode material - Google Patents

Abstract

PURPOSE:To provide a material, which costs low and is good on safety, instead of noble metals and perovskite double oxides by using a double oxide including spinel crystal structure as a suitable material for an air electrode of a solid electrolyte type fuel cell and an electrode of a solid electrolyte type oxygen sensor. CONSTITUTION:MxMn3-xO4 is used for a double oxide including spinel crystal structure. In this chemical formula, M represents at least one kind of substance selected among Ni, Cu, and Zn, while x is set to 0.1<=x<=1.5. A percentage content of spinel crystal structure is 50weight%, or more, and is desirably 70weight% or more, so that mutual contact between spinel particles is improved, and consequently, electrode performance is improved. Other materials but spinel crystal structure are included on condition that a spinel structure characteristic is not damaged. For example, the material includes following substances such as platinum and palladium for adding more element conductivity, zirconium oxide and cerium oxide for adding more ion conductivity, and glass group inorganic hinder for improving a contact property with a solid electrolyte.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode material, and more particularly to an air electrode for a solid electrolyte type fuel cell, and an electrode material suitable for an oxygen electrode such as an electrode for a solid electrolyte type oxygen sensor.

[0002]

2. Description of the Related Art Conventionally, platinum, gold, silver, and the like have been used as electrode materials for promptly causing electrochemical oxidation and reduction reactions of oxygen.
A single or a mixture of noble metals such as palladium and perovskite type complex oxides composed of lanthanum, strontium, calcium, iron, cobalt, nickel, manganese and the like are known. These materials are used as an air electrode for a solid oxide fuel cell and an electrode for an oxygen sensor because they have a property of adsorbing and desorbing oxygen, dissociation of oxygen molecules and ionization, and having conductivity. However, among the conventional electrode materials, the electrode material using a noble metal is expensive, and there is a problem in using it in large quantities. On the other hand, the performance of the electrode material using the perovskite type double oxide is significantly deteriorated in a reducing gas atmosphere, and there is a problem particularly when it is used as an electrode for an oxygen sensor.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a novel inexpensive and excellent alternative to a noble metal and a perovskite type complex oxide. In providing the electrode material. Other objects and effects of the present invention will be apparent from the following description.

[0004]

The above-mentioned object is achieved by an electrode material composed of a double oxide containing a spinel type crystal structure represented by the following general formula (1). M _X Mn _3-X O ₄ (1) (where M is at least one element selected from Ni, Cu and Zn, and if 0.1 ≦ X ≦ 1.5) is there.)

The spinel-type metal-manganese composite oxide electrode of the present invention has a catalytic action for the electrochemical oxidation / reduction reaction of oxygen, and is a so-called mixture having both electron conductivity and oxygen ion conductivity. It is a conductive material. Due to this mixed conductivity, the adsorption and desorption reaction of oxygen becomes easy,
The energy accompanying the reaction can be taken out or supplied as electric energy by the movement of electrons.

The first element constituting the electrode of the present invention is manganese, and the second element is at least one element selected from Ni, Cu and Zn. An electrode composed of an element other than the above elements is not suitable as the electrode of the present invention because mixed conductivity does not appear or its conductivity is too low.

In the above general formula (1) M _x Mn _3-X O ₄ of the present invention, when X is less than 0.1 or exceeds 1.5, both the oxygen ion conductivity and the electron conductivity are reduced, and the electrode of the present invention is obtained. Is not suitable for Therefore, the range of X in the present invention is 0.1 ≦ X ≦ 1.5, preferably 0.3 ≦ X
≦ 0.8.

The spinel type crystal in the present invention means both a tetragonal spinel which is a low temperature stable phase and a cubic spinel which is a high temperature stable phase. The mixed conduction mechanism is present in both crystal systems. Therefore, these crystal systems may be used alone, or both crystal systems may be mixed and used.

The content of the spinel type crystal structure in the electrode material of the present invention is preferably 50% by weight or more, more preferably 70% by weight or more. If the content is too low, it becomes difficult to keep the mutual contact of the spinel particles, and therefore the performance as an electrode is poor, which is not preferable.

In the present invention, materials other than the spinel type crystal structure may be contained according to various purposes within a range not impairing the characteristics possessed by the spinel type. For example,
In order to further impart electron conductivity, platinum, palladium, gold,
Noble metals such as silver, zirconium oxide for further imparting oxygen ion conductivity, oxides such as cerium oxide and titanium oxide, and a glass-based inorganic binder for improving contact with a solid electrolyte such as zirconia. Can be mentioned.

The finer the particle size of the electrode material of the present invention is, the higher the activity is, which is preferable. However, if it is too small, it is difficult to synthesize and handle the particle size, and particle growth may occur depending on the use temperature, resulting in deterioration of performance. . Therefore, the preferable particle size is 0.01 μm to 10 μm.

The spinel type double oxide of the present invention is synthesized by a commonly used ceramic synthesizing method. For example, a method in which a predetermined amount of oxide is uniformly mixed using a pulverizing and mixing device such as a ball mill and then synthesized at a high temperature of about 1000 ° C. Alternatively, a method in which a predetermined amount of an aqueous solution of a metal salt is distilled or neutralized and coprecipitated, and then calcined at a temperature of about 800 ° C. for synthesis. Sol-gel method using alkoxide containing desired metal. Alternatively, there is a so-called CVD method in which an oxide is deposited at a high temperature using a gas containing a desired metal.

The spinel type double oxide electrode is also installed by using a commonly used electrode installation method. For example, it is directly applied to the substrate by brushing, baking, or by sputtering, CVD, thermal spraying, or the like.

【The invention's effect】

The electrode material of the present invention is a mixed conductive material having both oxygen ion conductive and electronic conductive mechanisms. Therefore, the adsorption and desorption of oxygen is facilitated, the oxygen molecule is ionized and its energy is converted into electric energy, and conversely, the electric energy is generated and the oxygen molecule is generated.
It can be consumed for the ionization of oxygen. Therefore, it is effective as an electrode material for a solid oxide fuel cell, an oxygen concentration detecting element and the like which requires such energy conversion. In addition, nickel, copper, zinc, and manganese are economically advantageous because they are cheaper than precious metals, and because they do not have a perovskite structure, they have advantages such as little deterioration due to reducing gas.

【Example】

 Example 1

(1) In the formula M _x Mn _3-X O ₄ , X is 0.6
Nickel oxide (NiO), copper oxide (CuO), zinc oxide (ZnO) and manganese oxide (MnO ₂ ) are weighed and mixed in a ball mill for 10 hours in a wet manner, then filtered and dried, and then air Ni atmosphere for 10 minutes at 1000 ℃ Ni _0.6 Mn
_2.4 O _4, Cu _0.6 Mn _2.4 O ₄ , Zn _0.6 Mn _2.4 O ₄ , Ni _0.2 Cu _0.2 Zn _0.2 Mn
_2.4 O ₄ spinel type complex oxide sample No. 4 1,
No. 2, No. 3 and No. Got 4. The obtained double oxide was pulverized again in methanol for 50 hours and then dried to obtain an electrode material. The above substance is a cubic spinel structure (confirmed from the diffraction peaks of surface indices (311), (220) and (400)) single phase, or a cubic spinel structure and a tetragonal spinel structure (face index). (31
It was confirmed from a powder X-ray that the mixed phase of (1), (113) and (202) diffraction peaks) was a mixed phase.

Diameter 4 doped with 6 mol% yttria
A slurry in which the above electrode material was dispersed in methanol on both surfaces of a zirconia disk having a thickness of 0 mm and a thickness of 1 mm had a diameter of 1
A brush was applied to 0 mm, and the electrode was dried and baked at 950 ° C. for 2 hours. Next, as shown in FIG. 1, the above disks were seal-bonded with an alumina tube and an inorganic adhesive, and platinum lead wires were installed on the respective electrodes.
An oxygen concentration cell type oxygen sensor element was produced. A nitrogen-balanced mixed standard gas containing 1% oxygen was flowed in an alumina tube at a flow rate of 150 cc / min to 700 ° C.
The electromotive force was measured. The opposite electrode is in contact with the atmosphere. The results are shown in Table 1. It was confirmed that the electrode of the present invention operates as an oxygen electrode.

[Table 1] Example 2

Various nitrates were dissolved in distilled water so that the electrode composition was as shown in Table 2, and then ammonia water was added dropwise to coprecipitate, filtered, dried, and then calcined at 900 ° C. for 5 hours in the air atmosphere to give spinel. Type complex oxide No. 5 to No. 35 was obtained. In addition, it was confirmed from the powder X-rays as in Example 1 that each composition had a cubic spinel structure single phase or a mixed phase with a tetragonal spinel structure.

Then, an electrode material was prepared in the same manner as in Example 1, coated on both sides of the zirconia disk, and baked. Next, install platinum lead wires on both electrodes,
The complex impedance in the atmosphere was measured in an electric furnace at 0 ° C. Complex impedance is S57 as FRA
20C (manufactured by NF Circuit Design Block) was measured using HA-501G (manufactured by Hokuto Denko) as a power source under the conditions of a frequency range of 1 mHz to 10 kHz and an applied voltage of 0.2V.

Table 2 shows these electrode resistances. The electrode resistance was obtained by Cole-Cole plot of the measurement result of the complex impedance, and the diameter of the third arc indicating the resistance value of the electrode portion was determined as the electrode resistance. For comparison, platinum sample N
o. 36 and perovskite oxide La _{0. 6} Sr _0.4 MnO ₃ Sample No. The same measurement was performed when 37 was used as an electrode.

From Table 2, it can be seen that the spinel type mixed oxide electrode of the present invention exhibits the same electrode resistance as platinum and perovskite type mixed oxide electrodes. This means that the electrode material of the present invention facilitates the equilibrium state of adsorption / desorption reaction of oxygen, dissociation, and ionization. Further, it can be seen that the electrode resistance is kept low in the range of 0.1 ≦ X ≦ 1.5.

[Table 2] Example 3

Spinel type complex oxides (M =
Ni) Sample No. A zirconia disk on which 1 and perovskite type complex oxide (La _0.6 Sr _0.4 MnO ₃ ) were installed was treated at 700 ° C. for 10 hours in a reducing gas atmosphere containing 15% of carbon monoxide (nitrogen balance). Then, an oxygen concentration cell type oxygen sensor element was prepared in the same manner as in Example 1 using the zirconia disk treated with reducing gas, and the electromotive force with respect to the oxygen concentration was measured to obtain the complex impedance in the same manner as in Example 2. It was measured.

As a result, the electromotive force value of the spinel type double oxide electrode was 63.3 mV, and the electromotive force of the perovskite type double oxide electrode was 38.1 mV.

On the other hand, the resistance value of the electrode portion obtained from the complex impedance measurement was 1.6 times that before the reducing gas treatment in the case of the spinel type mixed oxide electrode, whereas in the perovskite type mixed oxide electrode. The electrode resistance increased 100 times or more. It can be seen that the perovskite-type mixed oxide is greatly deteriorated by the reducing gas treatment, whereas the spinel-type mixed oxide electrode of the present invention is hardly deteriorated. Example 4

The spinel type complex oxide (M = Cu) sample No. 1 used in Example 1 was used. Zirconia powder (0.3 μm) doped with 2 and 3 mol of yttria was mixed at various ratios shown in Table 3 and baked on a zirconia disk in the same manner as in Example 1 to prepare a concentration cell type oxygen sensor element. The performance was evaluated. The evaluation conditions were a test gas concentration of 1% and a temperature of 650 ° C. The results are shown in Table 3.

[Table 3]

[Brief description of drawings]

FIG. 1 is an oxygen concentration cell type oxygen sensor according to the present invention.
It is explanatory drawing of an element.

Claims (1)

[Claims] 1. An electrode material comprising a double oxide containing a spinel type crystal structure represented by the following general formula (1). M _X Mn _3-X O ₄ (1) (where M is at least one element selected from Ni, Cu and Zn, and if 0.1 ≦ X ≦ 1.5) is there.)